NAME

SYNOPSIS

DESCRIPTION

The
patch
utility reads a source (patch)
file containing any of the three forms of
difference (diff) listings produced by the
diff
utility (normal, context or in the style of
ed)
and apply those differences to a file.
By default,
patch
reads from the standard input.

The
patch
utility attempts to determine the type of the
diff
listing, unless overruled by a
-c,
-e
or
-n
option.

If the patch
file contains more than one patch,
patch
will attempt to apply each of them as if they came from separate
patch files.
(In this case the name of the patch file must be determinable for each
diff
listing.)

OPTIONS

Save a copy of the original contents of each modified file,
before the differences are applied, in a file of the same
name with the suffix
.orig
appended to it.
If the file already exists, it will be overwritten;
if multiple patches are applied to the same file, the
.orig
file will be written
only for the first patch.
When the
-ooutfile
option is also specified,
file.orig
will not be created but, if
outfile
already exists,
outfile.orig
will be created.

-c

Interpret the patch file as a context difference
(the output of the utility
diff
when the
-c
or
-C
options are specified).

-d dir

Change the current directory to
dir
before processing as described in the EXTENDED DESCRIPTION section.

-D define

Mark changes with the C preprocessor construct:

#ifdef define
...
#endif

The option-argument
define
will be used as the differentiating symbol.

Read the patch information from the file named by the pathname
patchfile,
rather than the standard input.

-l

(The letter ell.)
Cause any sequence of blank characters
in the difference script to match any sequence of
blank characters
in the input file.
Other characters will be matched exactly.

-n

Interpret the script as a normal difference.

-N

Ignore patches where the differences have already been applied to the file;
by default, already-applied patches are rejected.

-o outfile

Instead of modifying the files (specified by the
file
operand or the difference listings) directly, write a copy
of the file referenced by each patch, with the appropriate
differences applied, to
outfile.
Multiple patches
for a single file will be applied to the intermediate
versions of the file created by any previous patches,
and will result in multiple,
concatenated versions of the file being written to
outfile.

-p num

For all pathnames in the patch file that indicate the
names of files to be patched, delete
num
pathname components from the beginning of each pathname.
If the pathname in the patch file is absolute,
any leading slashes are considered the first
component (that is,
-p 1
removes the leading slashes).
Specifying
-p 0
causes the full pathname to be used.
If
-p
is not specified, only the basename (the final
pathname component) is used.

-R

Reverse the sense of the patch script; that is,
assume that the difference
script was created from the new version to the old version.
The
-R
option cannot be used with
ed
scripts.
The
patch
utility attempts to reverse each portion of
the script before applying it.
Rejected differences will be saved in swapped format.
If this option is not specified, and until
a portion of the patch file is successfully applied,
patch
attempts to apply each portion in its reversed sense as well
as in its normal sense.
If the attempt is successful, the user
will be prompted to determine if the
-R
option should be set.

-r rejectfile

Override the default reject filename.
In the default case, the
reject file will have the same
name as the output file, with the suffix
.rej
appended to it.
See
Patch Application
.

OPERANDS

The following operand is supported:

file

A pathname of a file to patch.

STDIN

See the INPUT FILES section.

INPUT FILES

Input files must be text files.

ENVIRONMENT VARIABLES

The following environment variables affect the execution of
patch:

LANG

Provide a default value for the internationalisation variables
that are unset or null.
If
LANG
is unset or null, the corresponding value from the
implementation-dependent default locale will be used.
If any of the internationalisation variables contains an invalid setting, the
utility will behave as if none of the variables had been defined.

LC_ALL

If set to a non-empty string value,
override the values of all the other internationalisation variables.

LC_CTYPE

Determine the
locale for the interpretation of sequences of bytes of text data as
characters (for example, single- as opposed to multi-byte characters
in arguments and input files).

LC_MESSAGES

Determine the locale that should be used to affect
the format and contents of diagnostic
messages written to standard error
and informative messages written to standard output.

NLSPATH

Determine the location of message catalogues
for the processing of
LC_MESSAGES .

LC_TIME

Determine the locale for recognising
the format of file timestamps written by the
diff
utility in a context-difference input file.

ASYNCHRONOUS EVENTS

Default.

STDOUT

Not used.

STDERR

Used for diagnostic and informational messages.

OUTPUT FILES

The output of the
patch
utility,
the save files
(.orig
suffixes) and the reject files
(.rej
suffixes) will be text files.

EXTENDED DESCRIPTION

A patchfile may contain patching instructions for more than one file;
filenames are determined as specified in
Filename Determination
.
When the
-b
option is specified,
for each patched file, the original will be saved in a
file of the same name with the suffix
.orig
appended to it.

For each patched file, a reject file may also be created as noted in
Patch Application
.
In the absence of a
-r
option, the name of
this file will be formed by appending the suffix
.rej
to the original filename.

Patchfile Format

The patch file must contain zero or more lines of header information
followed by one or more patches.
Each patch must contain zero or more
lines of filename identification in the format produced by
diff-c,
and one or more sets of
diff
output, which are customarily
called hunks.

The
patch
utility recognises the following expression in the
header information:

Index: pathname

The file to be patched is named
pathname.

If all lines (including headers) within a patch begin with the
same leading sequence of
blank characters,
the
patch
utility will remove this sequence before proceeding.
Within each patch, if the type of difference is context, the
patch
utility recognises the following expressions:

*** filename timestamp

The patches arose from
filename.

--- filename timestamp

The patches should be applied to
filename.

Each hunk within a patch must be the
diff
output to change a line
range within the original file.
The line numbers for successive
hunks within a patch must occur in ascending order.

Filename Determination

If no
file
operand is specified,
patch
performs the following steps to obtain a pathname:

If the patch contains the strings
***
and
---,
the
patch
utility strips components from the beginning of each
pathname (depending on the presence or value of the
-p
option), then tests for the
existence of both files in the current directory (or
directory specified with the
-d
option).
If both files exist,
patch
assumes that no pathname can be obtained from this step.

If the header information contains a line with the string
Index:,
patch
utility strips components from the
beginning of the pathname (depending on
-p),
then tests for the existence of this file in the current directory
(or directory specified with the
-d
option).

If an
SCCS
directory exists in the current directory,
patch
will attempt to perform a
get-e
SCCS/s.filename
command to retrieve an editable version of the file.

If no pathname can be obtained by applying the previous steps,
or if the pathnames obtained do not exist,
patch
will write a prompt to standard output and
request a filename interactively from standard input.

Patch Application

If the
-c,
-e
or
-n
option is present, the
patch
utility will
interpret information within each hunk as a context difference, an
ed
difference or a normal difference, respectively.
In the absence of any of
these options, the
patch
utility determines the type of difference
based on the format of information within the hunk.

For each hunk, the
patch
utility begins to search for the
place to apply the patch at the line number at the beginning of
the hunk, plus or minus any offset used in applying the previous hunk.
If lines matching the hunk context are
not found,
patch
scans both forwards and backwards at least
1000 bytes for a set of lines that match the hunk context.

If no such place is found and it is a context difference, then another
scan will take place, ignoring the first and last line of context.
If that fails, the first two and last two lines of context will be ignored
and another scan will be made.
Implementations may search more extensively for installation locations.

If no location can be found, the
patch
utility will append the
hunk to the reject file.
The rejected hunk will be written in
context-difference format regardless of the format of the patch file.
If the input was a normal or
ed-style
difference, the reject file may contain differences
with zero lines of context.
The line numbers on the hunks in the
reject file may be different from the line numbers in the patch
file since they will reflect the approximate locations for the
failed hunks in the new file rather than the old one.

If the type of patch is an
ed
diff,
the implementation may accomplish the patching by invoking the
ed
utility.

EXIT STATUS

The following exit values are returned:

0

Successful completion.

1

One or more lines were written to a reject file.

>1

An error occurred.

CONSEQUENCES OF ERRORS

Patches that cannot be correctly placed in the file
will be written to a reject file.

APPLICATION USAGE

The
-R
option will not work with
ed
scripts because there is too little information to reconstruct
the reverse operation.

The
-p
option makes it possible to customise a patchfile to local
user directory structures without manually editing the patchfile.
For example, if the filename in the patch file was:

/curds/whey/src/blurfl/blurfl.c

Setting
-p 0
gives the entire pathname unmodified;
-p 1
gives:

curds/whey/src/blurfl/blurfl.c

without the leading slash,
-p 4
gives:

blurfl/blurfl.c

and not specifying
-p
at all gives:

blurfl.c .

When using
-b
in some file system implementations, the saving of a
.orig
file may produce unwanted results.
In the case of 12, 13 or 14-character filenames,
on file systems supporting 14-character maximum filenames, the
.orig
file will overwrite the new file.

EXAMPLES

None.

FUTURE DIRECTIONS

The IEEE PASC 1003.2 Interpretations Committee has forwarded concerns about
parts of this interface definition to the IEEE PASC Shell and Utilities Working Group
which is identifying the corrections.
A future revision of this specification will align with
IEEE Std. 1003.2b when finalised.